Apparatus for conversion of hydrocarbons

ABSTRACT

An apparatus for the catalytic conversion of hydrocarbons at short contact times, the apparatus including a transfer line reactor having a vertical riser portion, a crossover portion and a downcomer portion.

United States Patent 2 Robert W. Pfeiffer Bronxville, N.Y.

Jan. 23, 1970 Sept. 21, 1971 Pullman Incorporated Chicago, Ill.

Continuation-impart of application Ser. No. 719,052, Apr. 5, 1968, now Patent No. 3,492,221, dated Jan. 27, 1970.

Inventor Appl. No. Filed Patented Assignee APPARATUS FOR CONVERSION OF HYDROCARBONS 9 C1aims,4 Drawing Figs.

u.s. C1. 23/288 E, 23/288 8, 138/26, 208/153,208/155, 208/164, 285/47,285/55,285/156 Int. Cl B01j 9/16, F16 155/00,F16159/16 Field of Search 23/2883 S; 208/164, 153,155;285/156, 179, 47, 48, 55;

Primary Examiner-Joseph Scovronek Attorneys-John C. Quinlan and Margareta Le Maire 138/26 US, 30; 302/29 US, 51 US, 45

References Cited UNITED STATES PATENTS 4/1953 Jones 23/2883 8 X 1/1958 Wood et a1. 23/2883 S UX 10/1964 Wickham 23/2883 S X 7/1966 Baumann et a1. 23/288.3SX 10/1969 Luckenbach 23/2883 S X ABSTRACT: An apparatus for the catalytic conversion of hydrocarbons at short contact times, the apparatus including a transfer line reactor having a vertical riser portion, a crossover portion and a downcomer portion.

REGENERATED CATALYST 3 ,8 a

SPENT CATALYST TO REGENERATOR PATENTEDSEP21 l97| sum 1 or 2 O T TR R D B E LN M MR6 w R A w m 3 Ell-O CE /.v -mw 4 m 6 EA 0 MR F R S ROBERT w PFEIFFER ATTORNEY I AGENT REGENERATED CATALYST 3 PATENTEUSEPZIW! 3 507,127

sum 2 [IF 2 REGENERATED CATALYST 157 HYDROCARBON FEED 158 SPENT CATALYST TO REGENERATOR 154 ROBERT W. PFEIFFER INVEIN'I'UR. 210W ATTORNEY AGENT APPARATUS FOR CONVERSION OF HYDROCARBONS This application is a continuation-in-part of pending application Ser. No. 719,052, filed Apr. 5, 1968, now U.S. Pat. No. 3,492,221, granted Jan. 27, 1970.

The present invention relates to an apparatus for conversion of hydrocarbons and more specifically to an apparatus for fluill catalytic cracking of relatively heavy hydrocarbons to high quality gasoline product.

In recent years, commercial catalytic cracking catalysts have been developed which are highly active and also exhibit superior selectivity towards the formation of desirable products such as gasoline at the expense of coke and light ends production. Examples of such catalysts are those of the types commonly called high alumina and molecular sieve catalysts. It has been found that maximum benefit is derived from these catalysts by reducing the time the catalyst is in contact with the hydrocarbons undergoing cracking in the reaction zone. For this reason, it is preferred to carry out the catalytic cracking operations employing so-called dilute or disperse phase cracking techniques, i.e., the catalyst is contacted with a hydrocarbon feed stream moving through the reaction zone at sufficiently high superficial velocities that the catalyst is carried along in said stream as a dilute suspension and with a minimum of back mixing.

In general, catalytic cracking of relatively high boiling hydrocarbons to form substantial quantities of materials boiling in the gasoline range is carried out in the following process sequence: hot regenerated catalyst is contacted with preheated hydrocarbon feed in a reaction zone under conditions suitable for cracking, the cracked hydrocarbon vapors are disengaged from the spent catalyst, which is subsequently fed to a stripping zone where it is contacted with a gasiform stripping agent, whereby volatile hydrocarbon material is stripped from the catalyst. The stripped catalyst is then transferred to a regeneration zone where it is regenerated by burning carbonaceous deposits from the catalyst using an oxygen-containing gas such as air, after which the regenerated catalyst is transferred to the reaction zone for reuse. The hydrocarbon material from the reaction zone and the stripping zone is transferred to a recovery system including suitable fractionation equipment for recovery of gaseous products, gasoline and one or more heavier fractions boiling above the gasoline range. The latter fractions may be withdrawn as products of the process or may at least in part be recycled to the reaction zone for further cracking.

The operating conditions employed to achieve catalytic cracking of hydrocarbons according to the aforementioned disperse phase cracking techniques include regenerator temperatures between about l,l and about l,500 F. and regenerator dilute phase pressures from about atmospheric pressure to about 35 p.s.i.g. The outlet of the disperse phase reaction zone can be operated in a temperature range above 850 F. and preferably between about 925 and about 1,000 F. or even higher. Suitable reaction zone pressures are between about p.s.i.g. and 50 p.s.i.g. The relative weights of catalyst and total hydrocarbons flowing through the elongated confined reaction zone, i.e., the so-called catalyst to oil ratio is preferably maintained at values ranging between about 2 and about 20 The length and volume of the elongated reaction zone should be sufficient to provide contact times therein from about 0.5 seconds to about 4 seconds or even higher, while the cross-sectional area of said zone is designed to result in superficial velocities of the suspension ranging between about ft./sec. and about 25 ft./sec. in the vicinity of the hydrocarbon feed inlet and between about ftJsec. and 60 ft./sec. at the reactor outlet. When combinations of these conditions are employed. it is possible to selectively crack the hydrocarbons at very high conversions, the conversion being the portion of the hydrocarbon feed boiling above the gasoline range which is converted to coke, gaseous products and liquid products boiling within the gasoline range. In present commercial installation the conversions are generally about 70 volume percent. However, there are considerable additional benefits to be had if the hydrocarbons were to be cracked at even higher conversions, e.g., in the range between about 75 and about percent, in a mechanically safe and relatively inexpensive reaction vessel.

The operating conditions employed in the stripping of spent catalyst in a stripping zone includes temperatures above about 825 F and preferably between about 900 and about 975 F and pressures ranging between about 10 p.s.i.g. and about 55 p.s.i.g. The amount of stripping medium relative to the catalyst circulation is advantageously maintained between about 1 and about 10 pounds per 1,000 pounds of circulated catalyst. Superficial velocities of the stripping medium are from about 0.5 ft./sec. to about 2.0 ft./sec.

In order to achieve the aforementioned desired high conversions in commercial installations processing large quantities of feed per day, the required length and volume of the confined reaction zone through which the dilute suspension of hydrocarbon is passed would be quite considerable, resulting in extremely tall structures, which from both a mechanical and a safety standpoint would be difficult to design and maintain and inherently would also be expensive. I

It is therefore an object of the present invention to provide a novel apparatus, the total height thereof being maintained at a reasonable level.

In accordance with the present invention there is provided in an apparatus for the conversion of hydrocarbons an elongated confined reaction conduit for passing a suspension of hydrocarbon vapors and catalyst therethrough comprising a substantially vertical riser portion, a first device for changing the direction of flow of the suspension exiting the riser portion, means for lateral passage of such suspension, a second device for changing the direction of flow of the suspension exiting said means and a substantially vertical downcomer portion depending from said second device. In one embodiment of the invention the aforementioned means consists of a crossover portion of the transfer conduit. In another embodiment the means consist of a first portion of a device for changing the direction of flow.

Means are provided for introducing freshly regenerated catalyst and hydrocarbon feed to a bottom section of the vertical riser. In one embodiment of the invention the outlet section of the downcomer is provided with means for separating the spent catalyst from the cracked hydrocarbon vapors. To accomplish this separation, such means can be one or more cyclones, the inlet of the primary cyclone being directly connected to the outlet of the downcomer. Other alternatives include a disengaging zone of a substantially larger cross-sectional area than that of the downcomer and enveloping the outlet of said downcomer, such that the velocity of the suspension upon discharge from the downcomer is drastically reduced, resulting in separation of the suspension into spent catalyst and cracked hydrocarbon vapors. The solids outlet of any of these separating means is in communication with a conventional stripping zone, which can be maintained in a separate vessel or, where applicable, in the bottom portion of the vessel containing the aforementioned disengaging zone. The vapor outlet from any of these separating means is in communication with a conventional product recovery zone, and stripped catalyst is passed to a vessel housing a conventional regeneration zone. The elongated confined transferreaction zone preferably includes an r sione i tan refra tory lining, which serves as the primary protection for the metal structure forming said zone.

In another embodiment of the invention, the outlet of the downcomer is buried beneath the surface of a fluidized dense bed of catalyst maintained in a vessel. Further cracking of the hydrocarbon vapors exiting the transfer conduit takes place in this bed. Additional hydrocarbons, e.g., hydrocarbons not suitable for short contact time cracking can also be fed to said dense bed.

The transfer-reaction conduit can be contained partially or completely within a vessel serving as a zone for further cracking and/or as a disengaging zone. This is particularly so when the reaction side of an existing commercial installation is to be revamped from dense fluidized bcu operations to dilute phase operations and the existing reaction vessel is therefore available. The size of such an existing vessel in conjunction with the desired feed throughput and the desired level of conversion, which affect the physical dimensions of the transferreactor conduit, are the major factors to consider when designing this system. For instance, when both throughput and conversion are to be increased substantially, it might be required or preferred to design a conduit-vessel system, in which a substantial portion of the conduit would be located outside the vessel. In extreme cases, only the very outlet section of the downcomer portion would be enclosed by the vessel.

The transfer conduit is provided with devices for changing the direction of flow and care should be exercised in their design since erosion will usually be at a maximum therein. It has been found that such erosion can be reduced substantially if the changes in direction of flow are about right angled, e.g., a vertical straight portion of the transfer conduit is closely followed by a horizontal straight portion, and if such portions are connected by appropriately designed devices. These devices function well when the aforementioned angle is between about 75 and about 105 degrees. One suitable design for such a connection is a so-called side-out tee, i.e., a tee used as elbow, entering run. The far end of the run is capped and is thus closed to flow. A more preferred design, however, is comprised of a truncated hollow cane, advantageously an oblique cone, extending from one such portion of the transfer conduit, the far end of the cone being its base of larger diameter and having a cap covering and closing said larger diameter base. In one embodiment an outlet in the conical surface is directly connected to another such portion of the transfer conduit in such a way that the projected axes of the respective portions are intersecting each other at angles in the range from about 75 to about 105 degrees. In a preferred embodiment of a device for changing the direction of flow, there is provided between the base of the cone and the cap an extension, such a hollow cylindrical extension of the same diameter as that of the base. The suspension enters through the smaller diameter area of the truncated cone and exits through the side outlet provided in the conical surface, the side outlet preferably having a cross-sectional area such that there is no substantial change in the velocity of the suspension as it flows through the device. The cone design has the advantage over the tee in that sharp edges at changes of directions of flow, which are particularly subject to erosion, have been removed from the direct line of impingement of a major portion of the solids suspension. The sudden change in direction of the highvelocity suspension causes solids to collect as a relatively dense suspension within the devices, especially in the respec tive closed portions thereof (i.e., in the far end of the run of the tee, or in the larger-diameter area of the cone or in the extension thereof), and said collected solids serve as a protective cushion on which the suspension impinges. The closed end portions of the aforementioned devices can be periodically opened for inspection and maintenance purposes without necessitating dismantling of any other part of the transfer conduit.

It is to be understood that the aforementioned devices can be used whenever it is desired to achieve at least one sharp change in the direction of flow of an erosive high-velocity suspension, and that the transfer conduit may not necessarily function as a reaction vessel. It is also to be understood that the cone can have more than one outlet in the conical surface to provide for branching of the material flowing into the cone. Such a design is particularly useful when it is desired to employ multiple transfer zones but the available space prohibits the full use thereof. Considerable savings in space can then be obtained by employing, for instance, a common riser portion and a cone with two or more outlets each connected to a crossover portion. Also, the outlet of one cone could be connected directly to the inlet of another such cone, thereby providing for an even greater immediate change in direction of flow where space is limited, i.e., with two such cone devices a sub stantially complete reversal in the direction of flow can be achieved without experiencing significant erosion problems.

In addition, the primary structures forming these devices can advantageously be enclosed within secondary protective structures of suitable designs, e.g. offset cylinders, where the annular space between a device and its corresponding secondary protective structure may be filled with an erosion resistant refractory material. Thus in case of an actual erosion failure in the primary structure forming the device, the secondary protective structure will continue to maintain the suspension within the transfer conduit. In such event plant operations need not be disrupted due to an erosion failure of the primary device, but can be continued for relatively long periods of time before plant shutdown for maintenance becomes necessary. It is to be understood that any other localized area of the transfer conduit found to be subject to severe erosion could also be enclosed within secondary protective structures similar to the ones previously described.

When employing the apparatus of the invention, a considerable reduction in actual height of the reaction zone is realized. Such a reduction in height can amount to as much as one-half or even more. There are several advantages of a reaction zone of reduced height, e.g., structures needed for support of extremely tall vertical vessels, having large length to diameter ratios, can be minimized or obviated. Also, the

overall plant layout can be considerably simplified, since one has almost complete freedom in selecting the elevation from ground level of the outlet of the downcomer portion of the transfer conduit. This is particularly so when only the reactor side of an existing commercial installation is to be revamped, other appurtenant facilities thereof being adequate, such as the stripper, regenerator, etc.

In order to provide a better understanding of the invention, reference will be had to the accompanying schematic drawings, which form a part of this specification.

In the drawings:

FIG. 1 is an elevated view of a specific example of the apparatus of the invention, said apparatus including a transfer conduit having a vertical riser, a crossover and a downcomer connected by conical devices.

FIG. 2 is a specific example of a conical device for changing the direction of flow of an erosive disperse phase suspension.

FIG. 3 is an elevated view of another specific example of the invention, wherein the transfer conduit system is comprised of a common riser portion, a cone with two outlets connected to the inlets of two cones and the outlets of the latter being connected to two respective downcomers.

FIG. 4 is an elevated view of still another embodiment of the invention, including a transfer conduit comprised of a riser portion, a crossover portion and a downcomer portion, all connected by side-out tees, the outlet of the downcomer being in direction communication with the inlet to a cyclone.

Referring now to FIG. 1, which depicts a transfer line cracking zone in communication with a separation zone and a stripping zone, a vertical riser portion 1 is provided having a hydrocarbon feed inlet 2 and a regenerated catalyst inlet 3. A dilute suspension of such vaporized hydrocarbon feed and regenerated catalyst flows through the vertical riser portion into the horizontal crossover portion 4 and subsequently into the vertical downcomer portion 6, which is, at the outlet thereof, in direction communication with means for separating the cracked vapors from the spent catalyst, in this embodiment the means being the vapor space 13 of vessel 12. Slots 7 are provided for the discharge of the suspension into vessel 12 and cap 8 closes off the extreme end of the downcomer. The respective riser-crossover and crossover-downcomer portions are connected by means of truncated oblique cones 9, which are closed at the far end of their runs by means of caps 11. All internal surfaces of these devices for changing the direction of flow and all connecting conduits thereto are lined with an erosion-resistant refractory material. The downcomer portion 6 enters vessel 12 through the top, said vessel serving as a separation zone and a stripping zone. The cracked vaporsspent catalyst suspension exiting slots 7 are disengaged in the vapor space 13 above the bed 14, which is contained in the lower portion of vessel 12. Stripping and fluidizing steam is provided to said bed and distributed by distributor 16. The lower portion of vessel 12 is further provided with baffles 17 to improve the stripping efi'iciency. Spent catalyst is withdrawn through conduit 18 and is transported to a regeneration vessel (not shown), where it is contacted with an oxygen-containing gas, such as air, to remove carbonaceous deposits from the catalyst. Cracked vapors and the additional hydrocarbon-containing vapors resulting from the stripping of the spent catalyst are passed to cyclones (not shown). for recovery of catalyst entrained in said vapors and then passed to a conventional product recovery zone (not shown).

FIG. 2 depicts in detail a cone device, similar to the ones shown on FIG. 1. This device is described hereinafter with respect to its connection to a vertical riser portion 52 and a crossover portion 53; however, it can equally well be employed to connect a horizontal crossover with a subsequent vertical downcomer. The device is comprised of a truncated oblique cone, which is connected at its lesser-diameter section to riser conduit 52 and at its oblique surface to the crossover section. A cylindrical extension 54 is provided at the larger diameter area of the cone which is capped by means of plate 56 or alternatively by other suitable closures such as a dished or ellipsoidal head. All internal metal surfaces of the cone device, as well as of all connective conduits are lined with an erosion-resistant refractory material 57, serving as primary protection therefore. A secondary protection is obtained by the enclosure of the device within a cylindrical structure 58, which is filled with additional erosion-resistant refractory material 59. The high-velocity upflowing solids-suspension from riser 52 causes solids to be collected and held in relatively dense suspension within the portion of the device extending above crossover conduit 53, and said solids act as a further protection against erosion in this area as the high-velocity suspension impinges thereon. The advantage of the device of FIG. 2 lies primarily in the removal of sharp projections 61 and 62 from the direct line of travel of the high-velocity eroding suspension, thereby considerably reducing erosion at such projections.

FIG. 3 shows another embodiment of the invention, wherein the major portion of the transfer conduit is located within a vessel 101, said vessel being identical to the one of FIG. 1. Thus, there is a stripping zone 102, equipped with baffles 103, steam distributor 104 and spent catalyst drawoff 106, said zone being located in the lower portion of the vessel and a disengaging zone 107 in the upper portion thereof. Cyclones and vapor outlet are not shown. A central riser portion 108, which is substantially vertical except for the first section thereof, is provided with regenerated catalyst inlet 109 and hydrocarbon inlet 111. The outlet of the riser is connected to the smaller diameter area of a truncated, symmetrical, hollow cone 112, which is capped at its far end by cap 113. In the conical surface there are two outlets, spaced 180 degrees apart. Each outlet is connected to the inlet of a truncated, hollow, oblique cone 114, such as the one shown in FIG. 2. In the conical surface of each of the oblique cones there is an outlet, which is connected to the top of a vertical downcomer 116, provided with discharge slots 118 and caps 119. In this embodiment of the invention the truncated, oblique cones serve as both the means for lateral transport and the means for changing the direction of flow.

The apparatus of FIG. 4 is still another embodiment of the invention. Again, vessel 151 is identical to the one of FIG. 1,

and it is equipped with baffles 152, stripping steam distributor 153, spent catalyst drawoff 154, cyclones 155 (only one shown) and a vapor drawoff (not shown). A vertical, external riser 156 is provided, having regenerated catalyst inlet 157 and hydrocarbon feed inlet 158. The crossover portion 159 enters vessel 151 through the side of said vessel, and the internal downcomer portion 161 is directly connected to an inlet to cyclone 155, which is equipped with dipleg 162'for discharge 0 spent catalyst to the stripper bed. Side out tees 163 are provided for changing the direction of flow of the suspension of hydrocarbon vapors and catalyst. The tees are capped at the far end of their runs by means of caps 164, and the tees are protected by means of secondary protective structures 166. The vapors leaving the bed maintained in the lower portion of the vessel are also passed to cyclone 155 for recovery of entrained catalyst.

It will be obvious to those skilled in the art, that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the in vention includes all such modifications.

What is claimed is:

1. In an apparatus for the conversion of hydrocarbons, an elongated transfer line reactor for passing a suspension of hydrocarbon vapors and catalyst therethrough under reaction conditions which comprises:

a substantially vertical riser portion having at the lower end.

thereof catalyst inlet means and oil inlet means;

a first device for sharply changing the direction of flow of the suspension exiting the riser portion;

means for lateral passage of the suspension;

a second device for sharply changing the direction of flow of the suspension exiting said means;

a substantially vertical downcomer portion depending from said second device for passage of the suspension from said second device;

means for separating catalyst from hydrocarbon vapors at the lower end of the vertical downcomer portion;

means for passing the catalysts to a stripper, and

means for passing the vapors to a product recovery zone.

2. An apparatus according to claim 1 in which said means for lateral transport is a lateral crossover portion.

3. An apparatus according to claim 1, in which said first device is provided with at least two outlets, each of said outlets being in direct communication with means for lateral passage of the suspension followed by a second device for changing the direction of flow of suspension exiting said means and a substantially vertical downcomer portion.

4. An apparatus according to claim 1, in which a vessel is provided which contains therewithin at least the outlet of the downcomer of said elongated conduit.

5. An apparatus according to claim 1, in which said means for separating the catalyst from the hydrocarbon vapors is a cyclone.

6..An apparatus according to claim 4, in which the outlet section of the downcomer is an apertured conduit.

7. An apparatus according to claim 4, in which the riser portion and the crossover portion are external to the vessel.

8. An apparatus according to claim 4, in which the riser portion and a first section of the crossover portion are external to the vessel and the remaining section of the crossover portion and the downcomer portion are contained within the vessel.

9. An apparatus according to claim 4, in which the crosssectional area of the vessel is substantially larger than that of the downcomer to provide for a rapid reduction in the velocity of the suspension upon discharge from the downcomer. 

2. An apparatus according to claim 1 in which said means for lateral transport is a lateral crossover portion.
 3. An apparatus according to claim 1, in which said first device is provided with at least two outlets, each of said outlets being in direct communication with means for lateral passage of the suspension followed by a second device for changing the direction of flow of suspension exiting said means and a substantially vertical downcomer portion.
 4. An apparatus according to claim 1, in which a vessel is provided which contains therewithin at least the outlet of the downcomer of said elongated conduit.
 5. An apparatus according to claim 1, in which said means for separating the catalyst from the hydrocarbon vapors is a cyclone.
 6. An apparatus according to claim 4, in which the outlet section of the downcomer is an apertured conduit.
 7. An apparatus according to claim 4, in which the riser portion and the crossover portion are external to the vessel.
 8. An apparatus according to claim 4, in which the riser portion and a first section of the crossover portion are external to the vessel and the remaining section of the crossover portion and the downcomer portion are contained within the vessel.
 9. An apparatus according to claim 4, in which the cross-sectional area of the vessel is substantially larger than that of the downcomer to provide for a rapid reduction in the velocity of the suspension upon discharge from the downcomer. 